1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method for flattening a semiconductor substrate or other object to be polished by chemical mechanical polishing.
2. Description of the Related Art
In the process of production of a semiconductor device, for example, a polishing apparatus using chemical mechanical polishing is used for flattening the uneven surface resulting from the multilayer structure of the semiconductor device. An example of this polishing apparatus is shown in FIG. 1 and FIG. 2.
A polishing apparatus 101 shown in FIG. 1 and FIG. 2 is provided with a polishing plate 121 which is rotatably held by a shaft 122 and to a front surface of which a polishing pad 111 is bonded, a polishing head 103 which is rotatably held by a shaft 103 arranged facing the polishing pad 111, and a slurry feed nozzle 131 for feeding a mixture 141 of a polishing agent (slurry) made of a mixture of for example potassium hydroxide (KOH) and silicon dioxide (SiO2) and pure water onto the polishing pad 111.
A polishing head 102 of the polishing apparatus 101, as shown in FIG. 2, is formed with a recessed holder 102a for holding a wafer W. The wafer W is held at this holder 102a via for example a backing film for holding the wafer W at the holder 102a. 
The polishing apparatus 101 feeds the mixture 141 of the slurry and the pure water from the slurry feed nozzle 131 onto a center portion of the polishing pad 111 and makes the polishing head 102 and the polishing plate 121 rotate while pressing the wafer W held at the polishing head 102 against the polishing pad 111 with a predetermined pressing force P.
The mixture 141 of the slurry and pure water disperses toward the outer circumference by the rotation of the polishing pad 111 and enters between the polishing pad 111 and the wafer W, whereby the wafer W is flattened by chemical mechanical polishing.
However, in the polishing apparatus 101 having the above configuration, in order to interpose a sufficient amount of slurry between the polishing pad 111 and the wafer W, it is necessary to continuously feed the slurry from the slurry feed nozzle 131, so the amount of consumption of the slurry is increased.
The cost of the slurry is relatively high, so if the amount of consumption of the slurry is increased, there is the disadvantage that the running cost (COO: cost of ownership) of the polishing apparatus 101 is increased.
On the other hand, since the slurry is a mixture of potassium hydroxide (KOH) and silicon dioxide (SiO2), it naturally easily forms hydrogen bondsxe2x80x94resulting in an increase in the particle size of the slurry.
The slurry having the increased particle size is apt to cause polishing scratches (microscratches and macroscratches) on the wafer W during polishing, therefore there was the disadvantage that the percentage of defective wafers W increased and the yield was lowered.
An object of the present invention is to provide a polishing apparatus using chemical mechanical polishing which is capable of reducing the amount of consumption of the polishing agent and capable of reducing the scratches caused on the object to be polished due to an increase of the particle size in the polishing agent and a polishing method using the same.
According to a first aspect of the present invention, there is provided a polishing apparatus which presses together and makes move relative to each other an object to be polished held at a polishing head and a polishing pad in a state where a polishing agent is interposed between a polishing surface of the object and the polishing pad so as to flatten the polishing surface of the object by chemical mechanical polishing, the polishing head comprising; a polishing agent receiving unit for receiving the polishing agent, a holding means for holding the object to be polished in a holding recess in the polishing head, a contact portion which is positioned at the periphery of the holding recess and is fully contacted to the polishing pad to define a closed space for positioning the polishing agent between the polishing surface of the object to be polished and the polishing pad, a polishing agent feed control means for controlling the feed and the step of the polishing agent from the polishing agent receiving port into the closed space in response to the amount of the polishing agent in the closed space.
Preferably, the polishing agent feed control means comprises a feed port for feeding the polishing agent from the polishing agent receiving portion into the closed space, and a valve means provided with a valve for opening and closing the feed port.
According to a second aspect of the present invention, there is provided a polishing apparatus which presses together and makes move relative to each other a polishing head and a polishing pad in a state where a polishing agent is interposed between a polishing surface of an object to be polished held by the polishing head and the polishing pad so as to flatten the polishing surface of the object by chemical mechanical polishing, the polishing apparatus comprising a vibration imparting means for imparting vibration to the polishing agent.
According to a third aspect of the present invention, there is provided a polishing method in which an object to be polished held at a polishing head and a polishing pad are pressed together and are made move relative to each other in a state where a polishing agent is interposed between a polishing surface of the object polished and the polishing pad so as to flatten the polishing surface by chemical mechanical polishing, the method comprising the steps of defining a closed space between the polishing surface of the object polished and the polishing pad and polishing the polishing surface in a state wherein the polishing agent kept in the closed space.
According to a fourth aspect of the present invention, there is provided a polishing method in which a polishing head and a polishing pad are pressed together and are made move relative to each other in a state where a polishing agent is interposed between a polishing surface of an object to be polished held by the polishing head and the polishing pad so as to flatten the polishing surface by chemical mechanical polishing, the method a step of comprising imparting vibration to the polishing agent.
According to the present invention, when the polishing agent is fed to the polishing agent receiving portion in a state where the contact portion of the polishing head is in full contact with the polishing pad, it is fed into the closed space defined by the contact portion, the polishing pad, and the polishing surface of the object to be polished by the polishing agent feed control means.
When the polishing agent is filled in the closed space, the polishing agent feed control means stops the feed of the polishing agent to give a state where the polishing agent is held in the closed space.
The polishing head and the polishing pad are made to move relative to each other in this state, whereby the polishing surface of the object to be polished is flattened by chemical mechanical polishing.
Further, by applying ultrasonic vibration to the polishing agent, even if the particle size of the polishing agent has increase, the particle size in the polishing agent can be reduced by the ultrasonic vibration, the particle size can equalized, and the formation of macroscratches or microscratches on the polishing surface of the object to be polished can be suppressed.